feat(apparmor): add support for optionally specifying a loaded apparmor profile to use for a process

Author: bleggett

src/apparmor.rs

@@ -0,0 +1,28 @@
+//! AppArmor profile transition for the workload process.
+
+use std::io::Write;
+
+/// Stage an AppArmor profile transition that takes effect on the next `execve`
+/// (the kernel's `aa_change_onexec` interface).
+///
+/// The named profile must already be loaded in the kernel. Writing an un-loaded/unknown
+/// profile name here will cause the next `execve` to fail with `-ENOENT`.
+/// Must be called after `PR_SET_NO_NEW_PRIVS` and before `execvpe()`.
+///
+/// The command must reach the kernel in a single `write(2)`, so it is formatted
+/// into one buffer. Writes to the per-LSM attr node `/proc/self/attr/apparmor/exec`
+/// (present on Linux 5.1+), and falls back to the pre-5.1 global node `/proc/self/attr/exec`.
+pub fn change_onexec(profile: &str) -> std::io::Result<()> {
+    let cmd = format!("exec {profile}");
+    let mut file = match std::fs::OpenOptions::new()
+        .write(true)
+        .open("/proc/self/attr/apparmor/exec")
+    {
+        Ok(file) => file,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => std::fs::OpenOptions::new()
+            .write(true)
+            .open("/proc/self/attr/exec")?,
+        Err(e) => return Err(e),
+    };
+    file.write_all(cmd.as_bytes())
+}

src/config.rs

@@ -86,6 +86,12 @@ pub struct ExecutableSpec {
     #[serde(default)]
     pub seccomp: Option<SeccompFilter>,
 
+    /// An optional AppArmor profile name to transition to on `execve`. The named
+    /// profile must already be loaded in the kernel. Staged after
+    /// `PR_SET_NO_NEW_PRIVS`, before `execvpe()`.
+    #[serde(default)]
+    pub apparmor: Option<String>,
+
     /// An optional out-of-memory score adjustment value.
     pub oom_score_adj: Option<i32>,
 }

src/lib.rs

@@ -1,3 +1,4 @@
+pub mod apparmor;
 pub mod caps;
 pub mod cgroup;
 pub mod config;

src/wrap.rs

@@ -725,6 +725,11 @@ impl ExecutableSpec {
             unsafe { filter.install()? };
         }
 
+        if let Some(profile) = &self.apparmor {
+            crate::apparmor::change_onexec(profile)
+                .map_err(|e| anyhow!("failed to set AppArmor profile {profile:?}: {e}"))?;
+        }
+
         // The Rust runtime ignores SIGPIPE (SIG_IGN) process-wide, and that
         // disposition is inherited across execve. Restore SIG_DFL so the
         // workload sees the standard broken-pipe behaviour, matching runc/crun.